Data reproducing method and device reproducing data according to a viterbi decoding algorithm using an average value of a reproduction signal

ABSTRACT

A data reproducing method reproduces data corresponding to a state-transition pass selected as being most likely according to a Viterbi decoding algorithm from a reproduction signal supplied from a recording medium. The data reproducing method comprises the steps of detecting at least one state of the reproduction signal according to data used for selecting the state-transition pass, calculating an average value of the reproduction signal in the state detected by the step of detecting, and following a fluctuation amount of a direct current component of the reproduction signal according to the average value.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to a data reproducingmethod, a data reproducing device and a magneto-optical disk device,more particularly, to a data reproducing method, a data reproducingdevice and a magneto-optical disk device which use apartial-response/maximum-likelihood (PRML) detecting method.

[0003] 2. Description of the Related Art

[0004] For example, a magneto-optical disk device has been implementedinto various fields such as in recording and reproduction ofpicture/image information and in recording and reproduction of varioussorts of code data for computers, due to its high capacity, low cost andhigh reliability. Such a magneto-optical disk device is expected to havean even higher capacity; accordingly, this requires a data reproducingmethod that can with high accuracy reproduce data recorded with highdensity.

[0005] There is a method for reproducing data with high accuracyincluding the processes of recording data in a magneto-optical disk bymodulating the data into a so-called partial response (PR) waveform,sampling signals reproduced from the magneto-optical disk at apredetermined interval, and thereafter detecting most likely data by aso-called Viterbi detector (a maximum-likelihood data detector).

[0006] For example, a data reproducing system of a magneto-optical diskdevice has enhanced its reproducing capability by calculating afluctuation amount (hereinafter referrer to as an offset amount) ofdirect current components of reproduction signals of data beingreproduced from a magneto-optical disk, and feeding back the calculatedoffset amount to an expected value of a PRML reproducing system.

[0007]FIG. 1 shows an example of a structure of a data reproducingsystem 100. In FIG. 1, an analog-to-digital converter 101 is suppliedwith an analog reproduction signal reproduced from a magneto-opticaldisk, for example, and then converts the analog reproduction signal intoa digital signal. A digital equalizer 102 shapes the waveforms of thedigital signal supplied from the analog-to-digital converter 101, andthen supplies sampled values to a Viterbi detector (a maximum-likelihooddetector) 103.

[0008] The Viterbi detector 103 detects recorded data from the sampledvalues of the analog reproduction signal supplied from theanalog-to-digital converter 101 via the digital equalizer 102 accordingto a Viterbi decoding algorithm.

[0009] The sampled values of the analog reproduction signal are suppliedto a branch-metric calculation unit (hereinafter referred to as a BM)104 of the Viterbi detector 103. The BM 104 calculates a branch-metricvalue (hereinafter referred to as a BM value) that is a differencebetween each of sampled values yt supplied thereto and an expectedvalue. The expected value is a value depending on a PR waveform, and isa value that the analog reproduction signal could essentially assume.The BM value is calculated for each expected value when the sampledvalue yt is supplied.

[0010] An add-compare-select unit (hereinafter referred to as an ACS)105 adds each of the above-mentioned BM values to a pass-metric value(hereinafter referred to as a PM value) of one clock before that isstored in a pass-metric memory (hereinafter referred to as a PMM) 106,and compares every two PM values after the addition. Then, the ACS 105selects the smaller of the every two PM values as a new PM valueaccording to the comparison result, and then stores the selected PMvalue in the PMM 106. Selecting the smaller PM value in this way meansselecting a state-transition pass. That is, the ACS 105 always selects astate-transition pass with the minimum PM value.

[0011] A pass memory (hereinafter referred to as a PM) 107 is suppliedfrom the ACS 105 with data (binary data) corresponding to the passesselected as described above. The PM 107 shifts the data corresponding toeach of the selected passes one by one, and in this course, weeds outdata corresponding to each of unselected passes one by one. Then, the PM107 outputs data corresponding to the surviving pass as a demodulatedsignal.

[0012] On the other hand, the ACS 105 supplies the selected PM values toa minimum-value selector 108. The minimum-value selector 108 selects theminimum PM value, and then supplies the selected PM value to anoffset-amount detector 109. The offset-amount detector 109 calculates anoffset amount according to the supplied PM value by using a slidingaverage method, for example. The data reproducing system 100 shown inFIG. 1 feeds back the calculated offset amount to the expected value ofa PRML reproducing system by adding the calculated offset amount to theexpected value and supplying the expected value including the offsetamount to the BM 104.

[0013]FIG. 2 shows another example of a structure of the datareproducing system 100. In FIG. 2, the digital equalizer 102 shapes thewaveforms of the digital signal supplied from the analog-to-digitalconverter 101, and then supplies sampled values to the Viterbi detector103 and a comparator 111. The comparator 111 is supplied with not onlythe sampled values of the analog reproduction signal but also a totalvalue of an offset amount from the offset-amount detector 109 and athreshold value.

[0014] The comparator 111 compares the sampled values supplied theretowith the total value of the offset amount and the threshold value, andthen supplies the comparison results to a state detector 112. The statedetector 112 judges the state of the sampled values on the basis of thecomparison results supplied thereto, and then supplies the judgmentresults to the offset-amount detector 109 and arespective-expected-value calculator 113.

[0015] The respective-expected-value calculator 113 feeds back theoffset amount to the expected value of a PRML reproducing system bycalculating respective expected values according to the suppliedjudgment results and supplying the calculated respective expected valuesto the BM 104. It is noted that the offset-amount detector 109calculates the offset amount according to the judgment results suppliedfrom the state detector 112.

[0016]FIG. 3 shows still another example of a structure of the datareproducing system 100. In FIG. 3, the digital equalizer 102 shapes thewaveforms of the digital signal supplied from the analog-to-digitalconverter 101, and then supplies sampled values to the Viterbi detector103 and a shift register 114. The shift register 114 delays the sampledvalues of the analog reproduction signal by a predetermined time, andsupplies the delayed to one terminal of an AND circuit 116.

[0017] On the other hand, the PM 107 outputs data corresponding to thesurviving pass as a demodulated signal, and also supplies thedemodulated signal to a state detector 115. The state detector 115judges the state of the sampled values on the basis of the demodulatedsignal supplied thereto, and then supplies the judgment results to theother terminal of the AND circuit 116.

[0018] The AND circuit 116 calculates logical products of the sampledvalues supplied from the shift register 114 and the judgment resultssupplied from the state detector 115, and then supplies the calculationresults to the respective-expected-value calculator 113. Therespective-expected-value calculator 113 feeds back an offset amount toan expected value of a PRML reproducing system by calculating respectiveexpected values according to the supplied calculation results andsupplying the calculated respective expected values to the BM 104.

[0019] However, the data reproducing system 100 shown in FIG. 1 cannotcorrectly select the minimum PM value when the difference between asampled value and an expected value is large. Therefore, the datareproducing system 100 shown in FIG. 1 problematically miscalculates anoffset amount in some cases.

[0020] There is also a problem that the data reproducing system 100shown in FIG. 2 has to have an augmented circuit scale for comparing athreshold value with a sampled value. Additionally, the data reproducingsystem 100 shown in FIG. 2 involves a problem that it is difficult todetermine a threshold value since the threshold value itself is requiredto follow an offset amount.

[0021] The data reproducing system 100 shown in FIG. 3 suffers a problemthat utilizing the demodulated signal output from the PM 107 entails adelay corresponding to the time required to perform the process in thePM 107 so as to delay the feedback to the expected value. In addition,since the data reproducing system 100 shown in FIG. 3 uses thedemodulated signal output from the PM 107, the data reproducing system100 requires the shift register 114 for delaying the sampled values.Therefore, there is also a problem that the data reproducing system 100shown in FIG. 3 has to have an enlarged circuit scale.

SUMMARY OF THE INVENTION

[0022] It is a general object of the present invention to provide animproved and useful data reproducing method, a data reproducing deviceand a magneto-optical disk device in which the above-mentioned problemsare eliminated.

[0023] A more specific object of the present invention is to provide adata reproducing method, a data reproducing device and a magneto-opticaldisk device which are able to calculate an accurate offset amountwithout increasing a circuit scale of a data reproducing system, and areable to have an expected value of a PRML reproducing system immediatelyfollow a fluctuation amount (the offset amount) of direct currentcomponents.

[0024] In order to achieve the above-mentioned objects, there isprovided according to one aspect of the present invention a datareproducing method for reproducing data corresponding to astate-transition pass selected as being most likely according to aViterbi decoding algorithm from a reproduction signal supplied from arecording medium, the method comprising the steps of:

[0025] detecting at least one state of the reproduction signal accordingto data used for selecting the state-transition pass;

[0026] calculating an average value of the reproduction signal in thestate detected by the step of detecting; and

[0027] following a fluctuation amount of a direct current component ofthe reproduction signal according to the average value.

[0028] Additionally, in the data reproducing method according to thepresent invention, the step of detecting may include the steps of:

[0029] outputting data supplied to a pass memory of a Viterbi detectoras the data used for selecting the state-transition pass; and

[0030] producing a state signal indicating the above-mentioned stateaccording to the data used for selecting the state-transition pass.

[0031] Additionally, in the data reproducing method according to thepresent invention, the step of calculating may include the steps of:

[0032] judging the above-mentioned state according to the state signal;and

[0033] calculating the average value of the reproduction signal in thestate judged by the step of judging.

[0034] Additionally, in the data reproducing method according to thepresent invention, the step of following may include the steps of:

[0035] determining at least one expected value according to the averagevalue, the expected value being used in the Viterbi decoding algorithm;and

[0036] supplying the expected value to a Viterbi detector.

[0037] Additionally, in the data reproducing method according to thepresent invention, the step of following may include the step of:

[0038] adjusting the fluctuation amount of the direct current componentaccording to the average value.

[0039] Additionally, in the data reproducing method according to thepresent invention, the above-mentioned state may be one of a peakportion, a center portion and a bottom portion of the reproductionsignal.

[0040] The data reproducing method according to the present inventiondetects at least one state (such as a peak portion, a center portion ora bottom portion) of a reproduction signal according to data used forselecting a state-transition pass, and then calculates an average valueof the reproduction signal in such a state so as to calculate afluctuation amount of a direct current component of the reproductionsignal. That is, since the data reproducing method according to thepresent invention does not detect a state of the reproduction signalaccording to data corresponding to a state-transition pass selected asbeing most likely, the data reproducing method can quickly calculate afluctuation amount of a direct current component of the reproductionsignal. In addition, since the data reproducing method according to thepresent invention detects at least one state of a reproduction signalaccording to data used for selecting a state-transition pass, the datareproducing method can calculate an accurate offset amount withoutincreasing a circuit scale of a data reproducing system.

[0041] In order to achieve the above-mentioned objects, there is alsoprovided according to another aspect of the present invention a datareproducing device for reproducing data corresponding to astate-transition pass selected as being most likely according to aViterbi decoding algorithm from a reproduction signal supplied from arecording medium, the device comprising:

[0042] a condition detector detecting at least one state of thereproduction signal according to data used for selecting thestate-transition pass;

[0043] an average circuit calculating an average value of thereproduction signal in the state detected by the condition detector; and

[0044] a follower following a fluctuation amount of a direct currentcomponent of the reproduction signal according to the average value.

[0045] Additionally, in the data reproducing device according to thepresent invention, the condition detector may be supplied with datasupplied to a pass memory of a Viterbi detector as the data used forselecting the state-transition pass so as to produce a state signalindicating the above-mentioned state according to the data used forselecting the state-transition pass.

[0046] Additionally, in the data reproducing device according to thepresent invention, the average circuit may judge the above-mentionedstate according to the state signal so as to calculate the average valueof the reproduction signal in the state.

[0047] Additionally, in the data reproducing device according to thepresent invention, the follower may determine at least one expectedvalue according to the average value, the expected value being used inthe Viterbi decoding algorithm, so as to supply the expected value to aViterbi detector.

[0048] Additionally, in the data reproducing device according to thepresent invention, the follower may adjust the fluctuation amount of thedirect current component according to the average value.

[0049] Additionally, in the data reproducing device according to thepresent invention, the above-mentioned state may be one of a peakportion, a center portion and a bottom portion of the reproductionsignal.

[0050] The data reproducing device according to the present inventiondetects at least one state (such as a peak portion, a center portion ora bottom portion) of a reproduction signal according to data used forselecting a state-transition pass, and then calculates an average valueof the reproduction signal in such a state so as to calculate afluctuation amount of a direct current component of the reproductionsignal. That is, since the data reproducing device according to thepresent invention does not detect a state of the reproduction signalaccording to data corresponding to a state-transition pass selected asbeing most likely, the data reproducing device can quickly calculate afluctuation amount of a direct current component of the reproductionsignal. In addition, since the data reproducing device according to thepresent invention detects at least one state of a reproduction signalaccording to data used for selecting a state-transition pass, the datareproducing device can calculate an accurate offset amount withoutincreasing a circuit scale of a data reproducing system.

[0051] In order to achieve the above-mentioned objects, there is alsoprovided according to still another aspect of the present invention amagneto-optical disk device for reproducing data according to astate-transition pass selected as being most likely according to aViterbi decoding algorithm from a reproduction signal supplied from arecording medium having data recorded according to a partial-responsewaveform, the device comprising:

[0052] a condition detector detecting at least one state of thereproduction signal according to data used for selecting thestate-transition pass, the data being supplied from a Viterbi detector;

[0053] an average circuit calculating an average value of thereproduction signal in the state detected by the condition detector; and

[0054] a follower following a fluctuation amount of a direct currentcomponent of the reproduction signal according to the average value.

[0055] The magneto-optical disk device according to the presentinvention detects at least one state (such as a peak portion, a centerportion or a bottom portion) of a reproduction signal according to dataused for selecting a state-transition pass, and then calculates anaverage value of the reproduction signal in such a state so as tocalculate a fluctuation amount of a direct current component of thereproduction signal. That is, since the magneto-optical disk deviceaccording to the present invention does not detect a state of thereproduction signal according to data corresponding to astate-transition pass selected as being most likely, the magneto-opticaldisk device can quickly calculate a fluctuation amount of a directcurrent component of the reproduction signal. In addition, since themagneto-optical disk device according to the present invention detectsat least one state of a reproduction signal according to data used forselecting a state-transition pass, the magneto-optical disk device cancalculate an accurate offset amount without increasing a circuit scaleof a data reproducing system.

[0056] Other objects, features and advantages of the present inventionwill become more apparent from the following detailed description whenread in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0057]FIG. 1 shows an example of a structure of a data reproducingsystem;

[0058]FIG. 2 shows another example of a structure of the datareproducing system;

[0059]FIG. 3 shows still another example of a structure of the datareproducing system;

[0060]FIG. 4 shows a structure of a data reproducing system according toan embodiment of the present invention;

[0061]FIG. 5 is an illustration for explaining examples of mergeconditions produced by combinations of conditions;

[0062]FIG. 6 is an illustration for explaining examples of pass merges;

[0063]FIG. 7 shows an example of a structure of a pass memory;

[0064]FIG. 8 is a timing diagram of an example of a pass-mergeabsolute-condition detector;

[0065]FIG. 9 shows an example of a structure of the pass-mergeabsolute-condition detector;

[0066]FIG. 10 is an illustration for explaining an example of anoperation of an automatic expected-value follower;

[0067]FIG. 11 shows an example of a structure of an automaticexpected-value allocating circuit; and

[0068]FIG. 12 shows a structure of a data reproducing system accordingto another embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0069] A description will now be given, with reference to the drawings,of embodiments according to the present invention.

[0070]FIG. 4 shows a structure of a data reproducing system according toan embodiment of the present invention. A data reproducing system 1shown in FIG. 4 comprises the analog-to-digital converter (Adc) 101, thedigital equalizer (Deq) 102, the Viterbi detector 103, and an automaticexpected-value follower 10. For example, an analog reproduction signalreproduced from a recording medium such as a magneto-optical disk via anoptical head is supplied to the analog-to-digital converter 101. It isnoted that the analog reproduction signal may be supplied to theanalog-to-digital converter 101 after being amplified by an amplifier.

[0071] The analog-to-digital converter 101 operates in synchronizationwith a clock signal from a clock generating circuit not shown in thefigure. Specifically, the analog-to-digital converter 101 samples theanalog reproduction signal supplied thereto, and then outputs thesampled values yt of the analog reproduction signal in synchronizationwith the clock signal.

[0072] The sampled values yt output one by one from theanalog-to-digital converter 101 in synchronization with the clock signalare supplied to the digital equalizer 102. The digital equalizer 102equalizes the waveforms of the sampled values yt into PR (1,1), and thensupplies the sampled values yt having the equalized waveforms to theViterbi detector 103. The Viterbi detector 103 outputs demodulatedsignal from the sampled values supplied thereto one by one according toa Viterbi decoding algorithm.

[0073] The Viterbi detector 103 comprises the BM 104, the ACS 105, thePMM 106 and the PM 107. The sampled values yt of the analog reproductionsignal are supplied to the BM 104 of the Viterbi detector 103. The BM104 calculates a BM value that is a difference between each of thesampled values yt supplied thereto and an expected value. The expectedvalue is a value depending on a PR waveform, and is a value that theanalog reproduction signal could essentially assume. The BM value iscalculated for each expected value when each one of the sampled valuesyt is supplied.

[0074] Hereinbelow, a description will be given, in order to facilitatethe understanding of the invention, of examples of PR (1,1) having threevalues and four states with a D-restriction, focusing on RLL (1,7) code,to which the present invention is not limited. It is noted that twosorts of the states can be omitted due to the D-restriction of the RLL(1,7) code. This is based on that an RZ signal having a fine pattern of“1010101010 . . . ” is, due to the D-restriction of the RLL (1,7) code,converted into an NRZ signal having a pattern of “1100110011 . . . ” inwhich the states of “010” and “101” are eliminated. Specifically, BMvalues BM2 and BM5 are eliminated.

[0075] In the above-mentioned case, the four possible states are S0(0,0), S1 (0,1), S2 (1,0) and S3 (1,1). The six possible expected valuesare P0, P1, P3, P4, P6 and P7. The BM 104 calculates BM values BM0, BM1,BM3, BM4, BM6 and BM7 that are differences between the sampled value ytand the expected values P0, P1, P3, P4, P6 and P7, by using thefollowing expressions (1) to (6).

BM0=|yt−P0|  (1)

BM1=|yt−P1|  (2)

BM3=|yt−P3|  (3)

BM4=|yt−P4|  (4)

BM6=|yt−P6|  (5)

BM7=|yt−P7|  (6)

[0076] The BM 104 supplies the ACS 105 with the BM values BM0, BM1, BM3,BM4, BM6 and BM7 calculated by using the expressions (1) to (6). The ACS105 adds the BM values BM0, BM1, BM3, BM4, BM6 and BM7 to PM values PM0to PM3 of one clock before, which are stored in the PMM 106, accordingto merge conditions, and calculates such that the PM values PM0 to PM3are integrated values of the minimum BM values BM0, BM3, BM4, BM6 andBM7 by using the following expressions (7) to (10).

PM0(t)=min[BM0+PM0(t−1), BM1+PM1(t−1)]  (7)

PM1(t)=BM3+PM3(t−1)  (8)

PM2(t)=BM4+PM4(t−1)  (9)

PM3(t)=min[BM6+PM2(t−1), BM7+PM3(t−1)]  (10)

[0077] Selecting the smaller PM value in this way means selecting astate-transition pass. That is, the ACS 105 always selects astate-transition pass with the minimum PM value. Namely, the ACS 105supplies the PM 107 with data (binary data) corresponding to theselected passes.

[0078] It is noted that BM0+PM0(t−1) of PM0(t) corresponds to atransition from the state S0 to the state S0, and BM1+PM1(t−1) of PM0(t)corresponds to a transition from the state S0 to the state S2. Inaddition, BM6+PM2(t−1) of PM3(t) corresponds to a transition from thestate S3 to the state S1, and BM7+PM3(t−1) of PM3(t) corresponds to atransition from the state S3 to the state S3.

[0079] There are four conditions represented by the followingexpressions (11) to (14) regarding relations among the elements inPM0(t) of the above expression (7) and PM3(t) of the above expression(10).

BM0+PM0(t−1)<BM1+PM1(t−1)]  (11)

BM0+PM0(t−1)≧BM1+PM1(t−1)]  (12)

BM6+PM2(t−1)<BM7+PM3(t−1)]  (13)

BM6+PM2(t−1)≧BM7+PM3(t−1)]  (14)

[0080] The merge conditions produced by combinations of these fourconditions are classified into four groups as shown in FIG. 5. FIG. 5 isan illustration for explaining examples of the merge conditions producedby the combinations of the conditions.

[0081]FIG. 5 shows a classification of a combination (1) of conditionsfulfilling the expressions (11) and (13), a combination (2) ofconditions fulfilling the expressions (12) and (13), a combination (3)of conditions fulfilling the expressions (11) and (14), and acombination (4) of conditions fulfilling the expressions (12) and (14),and also shows thereunder a trellis diagram of merge conditions producedby the combinations of the conditions. FIG. 5 also shows the mergeconditions produced by the combinations of the conditions, in otherwords, values of data D0 to data D3 corresponding to the selectedpasses.

[0082] For example, the data D0=0 corresponds to a pass from the stateS0 to the state S0, the data D0=1 corresponds to a pass from the stateS1 to the state S0, the data D1=1 corresponds to a pass from the stateS3 to the state S1, the data D2=0 corresponds to a pass from the stateS0 to the state S2, the data D3=0 corresponds to a pass from the stateS2 to the state S3, and the data D3=1 corresponds to a pass from thestate S3 to the state S3.

[0083] At least three out of the four groups of the merge conditionsproduced by the combinations (1) to (4) can be combined into eightgroups of pass merges as shown in FIG. 6. FIG. 6 is an illustration forexplaining examples of pass merges.

[0084]FIG. 6 shows combinations of the merge conditions produced bythree out of the combinations (1) to (4) shown in FIG. 5 and eightgroups of pass merges according to the combinations of the mergeconditions. It is noted that a mark “” in FIG. 6 indicates that a passis fixed to the corresponding state. For example, in a pass mergeaccording to a combination (1)→(1)→(1) of the merge conditions, a passis fixed to a state indicated by the mark “” due to a continuity of thepasses.

[0085] The PM 107 shifts the above-mentioned supplied data correspondingto each of the selected passes one by one, and in this course, weeds outdata corresponding to each of unselected passes one by one. Then, the PM107 outputs data corresponding to the surviving pass as a demodulatedsignal.

[0086]FIG. 7 shows an example of a structure of the pass memory. Thepass memory (PM) 107 shown in FIG. 7 is supplied with the data D0 to thedata D3 corresponding to the selected passes from the ACS 105. It isnoted that values of the data D0 to the data D3 are determined accordingto the merge conditions shown in FIG. 5. The PM 107 shown in FIG. 7comprises shift registers 20(0) to 20(3), selectors 21(0) to 21(3),shift registers 22(0) to 22(3), selectors 23(0) to 23(3), shiftregisters 24(0) to 24(3), . . . , selectors 25(0) to 25(3) arranged inparallel corresponding to the data D0 to the data D3, respectively. Thatis, the shift registers and the selectors are arranged alternately, inwhich the selectors select data to be supplied to the shift registersfrom among the data D0 to the data D3.

[0087] For example, when “1” is supplied to the data D3, the pass fromthe state S3 to the state S3 is judged to be likely according to themerge conditions shown in FIG. 5 so that all of the shift registerscorresponding to the data D3 regard the data D3 at the time (t−1) asdata at the time (t). On the other hand, when “0” is supplied to thedata D3, the pass from the state S2 to the state S3 is judged to belikely according to the state transitions shown in FIG. 5 so that all ofthe shift registers corresponding to the data D3 regard the data D2 atthe time (t−1) as data at the time (t).

[0088] Each of the shift resisters and the selectors performs theseoperations so that likely passes are left, and at the occurrence of thepass merges shown in FIG. 6, only the most likely pass is left. That is,after the occurrence of the pass merges shown in FIG. 6, the shiftregisters corresponding to each of the data D0 to the data D3 have thesame data. Therefore, when the PM 107 has a sufficient number of stages,data has to be output as a demodulated signal only from any one of theshift registers corresponding to each of the data D0 to the data D3. Itshould be noted that the data D1 is always supplied with “1”, and thatthe data D2 is always supplied with “0”, as shown in FIG. 5. This is dueto the D-restriction of the RLL (1,7) code. Hereinbelow, the data D0 tothe data D3 supplied from the ACS 105 are referred to as soft judgmentresults.

[0089] The automatic expected-value follower 10 comprises a shiftregister 11, a pass-merge absolute-condition detector 12, an AND circuit13, and a respective-expected-value calculator 14. It should be notedthat the respective-expected-value calculator 14 functions as a followerfollowing a fluctuation amount of a direct current component of thereproduction signal. The pass-merge absolute-condition detector 12 issupplied with the data D0 and the data D3 among the soft judgmentresults. The pass-merge absolute-condition detector 12 restricts theconditions on which pass merges occur.

[0090] Specifically, when the sampled value supplied from the digitalequalizer 102 via the shift register 11 is a peak value or a bottomvalue, the pass-merge absolute-condition detector 12 produces judgmentsignals merge1 and merge0 from the data D0 and the data D3, the judgmentsignals merge1 and merge0 judging whether the sampled value indicatesthe peak or the bottom.

[0091] The judgment signals merge1 and merge0 invalidate the judgmentsignals merge1 and merge0 themselves with respect to parts 30 in whichthe data D0 and the data D3 simultaneously change. This is because theparts in which the data D0 and the data D3 simultaneously change arehighly likely to be edges. In addition, parts encircled by ellipses 31and 32 are made to be the expected values of the Viterbi demodulationthrough averaging.

[0092]FIG. 9 shows an example of a structure of the pass-mergeabsolute-condition detector. For example, the data D3 indicated by FIG.8-(B) is supplied to an AND circuit 35, a negative logic AND circuit 36,an EOR circuit 37, a D-type flip-flop circuit (hereinafter referred toas a DFF) 39, and an EOR circuit 41. The data D0 indicated by FIG. 8-(C)is supplied to the AND circuit 35, the negative logic AND circuit 36,the EOR circuit 37, a DFF 40, and an EOR circuit 42.

[0093] The AND circuit 35 calculates a logical product of the data D3and the data D0, and then supplies data D3&D0 as indicated by FIG. 8-(D)to one terminal of an AND circuit 45. The negative logic AND circuit 36calculates a negative-logical product of the data D3 and the data D0,and then supplies data /D3&/D0 as indicated by FIG. 8-(E) to oneterminal of an AND circuit 46.

[0094] The EOR circuit 37 and a DFF 38 detect that the present data D3and the present data D0 are different and that the previous data D3 andthe previous data D0 are different, and then supplies the results toNAND circuits 43 and 44. That is, the EOR circuit 37 and the DFF 38detect that the data D3 and the data D0 are different on the basis oftwo states.

[0095] The DFF 39 and the EOR circuit 41 detect that the present data D3and the previous data D3 are different, and then supplies the result tothe NAND circuit 43. That is, the DFF 39 and the EOR circuit 41 detectan edge of the data D3. The DFF 40 and the EOR circuit 42 detect thatthe present data D0 and the previous data D0 are different, and thensupplies the result to the NAND circuit 44. That is, the DFF 40 and theEOR circuit 42 detect an edge of the data D0.

[0096] The NAND circuit 43 detects that the data D3 changes from “1” to“0”, and then supplies the detection result to the other terminal of theAND circuit 45. The NAND circuit 44 detects that the data D0 changesfrom “0” to “1”, and then supplies the detection result to the otherterminal of the AND circuit 46.

[0097] Accordingly, the AND circuit 45 outputs the judgment signalmerge1 indicated by FIG. 8-(F), for example. The AND circuit 46 outputsthe judgment signal merge0 indicated by FIG. 8-(G), for example.

[0098]FIG. 8 shows that, when the judgment signal merge0 is at a highlevel, the sampled value indicated by FIG. 8-(A) is a bottom value, andthat, when the judgment signal merge1 is at a high level, the sampledvalue indicated by FIG. 8-(A) is a peak value. The pass-mergeabsolute-condition detector 12 supplies the judgment signals merge1 andmerge0 to the AND circuit 13. The AND circuit 13 is supplied with thesampled values from the digital equalizer 102 via the shift register 11.

[0099] Accordingly, the AND circuit 13 judges from the judgment signalsmerge1 and merge0 whether the sampled value indicates the peak or thebottom, and then supplies the judgment result to therespective-expected-value calculator 14. The respective-expected-valuecalculator 14 calculates a bottom value, a peak value and a centervalue, for example, and then uses the bottom value, the peak value andthe center value to determine each of the expected values P0 to P7. Eachof the expected values P0 to P7 determined herein is fed back to theViterbi detector 103.

[0100]FIG. 10 is an illustration for explaining an example of anoperation of the automatic expected-value follower. It is noted thatFIG. 10 shows elements and parts necessary for explaining an operationof the automatic expected-value follower, leaving out elements and partsunnecessary for the explanation. It is also noted that the clock signalis supplied to each circuit that needs it.

[0101] In FIG. 10, a shift register 50 is supplied with the sampledvalue as indicated by FIG. 8-(A), and then supplies a selector 51 withthe sampled value adjusted in timing with the judgment signals merge1and merge0 such as indicated by FIG. 8-(F) and FIG. 8-(G). In FIG. 10,the shift register 50 supplies the selector 51 with the sampled valueadjusted in timing according to, for example, PR (1,1,0) or PR (0,1,1).The shift register 50 is also adaptable to a magneto-optical disk havingan ID unit and a MO unit that have different data frequencies.

[0102] The selector 51 is supplied with a selective signal 1 thatselects either PR (1,1,0) or PR (0,1,1), and then suppliesmoving-average circuits 53 and 54 with the sampled value adjusted to thetiming of PR (1,1,0) or PR (0,1,1) according to the selective signal 1.

[0103] A D0/D3 logic circuit 52 as a pass-merge absolute-conditiondetector is supplied with the data D0 and D3 from the ACS 105, and thenproduces the judgment signals merge1 and merge0 from the data D0 and thedata D3, as mentioned above. The D0/D3 logic circuit 52 supplies thejudgment signal merge0 to the moving-average circuit 53, and suppliesthe judgment signal merge1 to the moving-average circuit 54.

[0104] The moving-average circuit 53 uses the judgment signal merge0indicating the bottom value of the sampled value to calculate an averagebottom value of the part encircled by the ellipse 31 shown in FIG. 8,for example, by using the following expression (15).

Average(t)=[average(t−1)×(n−1)+sampled value]/n  (15)

[0105] In this expression, n is a number of the averaged samples, and isreferred to as an averaging number (aveno). It is noted that themoving-average circuit 53 calculates the average value when the judgmentsignal merge0 is at a high level, i.e., when the sampled value marks thebottom value.

[0106] The moving-average circuit 54 uses the judgment signal merge1indicating the peak value of the sampled value to calculate an averagepeak value of the part encircled by the ellipse 32 shown in FIG. 8, forexample, by using the above expression (15). The moving-average circuit54 calculates the average value when the judgment signal merge1 is at ahigh level, i.e., when the sampled value marks the peak value.

[0107] The average bottom value is supplied from the moving-averagecircuit 53 to an amplitude-adjusting preliminary calculator 55, asubtracting and limiting circuit 61, and an adding and dividing circuit62. The average peak value is supplied from the moving-average circuit54 to the amplitude-adjusting preliminary calculator 55, an adding andlimiting circuit 60, and the adding and dividing circuit 62. Theamplitude-adjusting preliminary calculator 55 comprises a subtracter 56,a divider 57, a divider 58, and a selector 59.

[0108] The subtracter 56 calculates an amplitude value from thedifference between the average peak value and the average bottom value,and then supplies the amplitude value to the divider 57 and the divider58. The divider 57 divides the amplitude value by 8, and then suppliesthe divided amplitude value to the selector 59. The divider 58 dividesthe amplitude value by 16, and then supplies the divided amplitude valueto the selector 59. The selector 59 supplies either of the amplitudevalue divided by 8, the amplitude value divided by 16, and 0 accordingto a selective signal 2 to the adding and limiting circuit 60, thesubtracting and limiting circuit 61 and the adding and dividing circuit62.

[0109] The adding and limiting circuit 60 adds the average peak valueand the value supplied from the selector 59, adjusts an upper limit of abit width thereof, and then outputs the adjusted value to a DFF 63. TheDFF 63 outputs the value supplied from the adding and limiting circuit60 as an average value of the peak values. The subtracting and limitingcircuit 61 subtracts the value supplied from the selector 59 from theaverage bottom value, adjusts an lower limit of a bit width thereof, andthen outputs the adjusted value to a DFF 64. The DFF 64 outputs thevalue supplied from the subtracting and limiting circuit 61 as anaverage value of the bottom values. The adding and dividing circuit 62adds the average bottom value and the value supplied from the selector59, divides the added value by 2, and then outputs the divided value toa DFF 65. The DFF 65 outputs the value supplied from the adding anddividing circuit 62 as an average value of the center values. Thesebottom value, peak value and center value can be used to determine eachof the expected values P0 to P7.

[0110]FIG. 11 shows an example of a structure of an automaticexpected-value allocating circuit. The automatic expected-valueallocating circuit shown in FIG. 11 is adaptable to PR (1,1,0) and PR(0,1,1), and outputs the expected values P0 to P7 for PR (1,1,0) or PR(0,1,1) according to the selective signal 1.

[0111] For example, the average value of the bottom values is suppliedto terminals selecting the expected values P0, P1 and P4, the averagevalue of the center values is supplied to terminals selecting theexpected values P1, P3, P4 and P6, and the average value of the peakvalues is supplied to terminals selecting the expected values P3, P6 andP7.

[0112]FIG. 12 shows a structure of a data reproducing system accordingto another embodiment of the present invention. A data reproducingsystem 2 shown in FIG. 12 is identical to the data reproducing systemshown in FIG. 4 except several elements and parts, and thus elements inFIG. 12 that are identical or equivalent to the elements shown in FIG. 4are referenced by the same reference marks, and will not be described indetail.

[0113] In FIG. 12, the respective-expected-value calculator 14 suppliesthe center value to a subtracter 15. Aside from the center value, thesubtracter 15 is supplied with a given value REG1 that is setarbitrarily by an MPU, etc. so as to detect an offset amount. Thesubtracter 15 supplies the difference between the center value and thegiven value REG1 to an adder 16 provided at a stage preceding thedigital equalizer 102. Accordingly, the data reproducing system 2 shownin FIG. 12 is capable of canceling the offset amount included in asampled value.

[0114] The present invention is not limited to the specificallydisclosed embodiments, and variations and modifications may be madewithout departing from the scope of the present invention.

[0115] The present application is based on Japanese priority applicationNo. 2001-063895 filed on Mar. 7, 2001, the entire contents of which arehereby incorporated by reference.

What is claimed is:
 1. A data reproducing method for reproducing datacorresponding to a state-transition pass selected as being most likelyaccording to a Viterbi decoding algorithm from a reproduction signalsupplied from a recording medium, the method comprising the steps of:detecting at least one state of said reproduction signal according todata used for selecting said state-transition pass; calculating anaverage value of said reproduction signal in said state detected by saidstep of detecting; and following a fluctuation amount of a directcurrent component of said reproduction signal according to said averagevalue.
 2. The data reproducing method as claimed in claim 1, whereinsaid step of detecting includes the steps of: outputting data suppliedto a pass memory of a Viterbi detector as said data used for selectingsaid state-transition pass; and producing a state signal indicating saidstate according to said data used for selecting said state-transitionpass.
 3. The data reproducing method as claimed in claim 2, wherein saidstep of calculating includes the steps of: judging said state accordingto said state signal; and calculating the average value of saidreproduction signal in said state judged by said step of judging.
 4. Thedata reproducing method as claimed in claim 1, wherein said step offollowing includes the steps of: determining at least one expected valueaccording to said average value, the expected value being used in saidViterbi decoding algorithm; and supplying said expected value to aViterbi detector.
 5. The data reproducing method as claimed in claim 1,wherein said step of following includes the step of: adjusting thefluctuation amount of the direct current component according to saidaverage value.
 6. The data reproducing method as claimed in claim 1,wherein said state is one of a peak portion, a center portion and abottom portion of said reproduction signal.
 7. A data reproducing devicefor reproducing data corresponding to a state-transition pass selectedas being most likely according to a Viterbi decoding algorithm from areproduction signal supplied from a recording medium, the devicecomprising: a condition detector detecting at least one state of saidreproduction signal according to data used for selecting saidstate-transition pass; an average circuit calculating an average valueof said reproduction signal in said state detected by said conditiondetector; and a follower following a fluctuation amount of a directcurrent component of said reproduction signal according to said averagevalue.
 8. The data reproducing device as claimed in claim 7, whereinsaid condition detector is supplied with data supplied to a pass memoryof a Viterbi detector as said data used for selecting saidstate-transition pass so as to produce a state signal indicating saidstate according to said data used for selecting said state-transitionpass.
 9. The data reproducing device as claimed in claim 8, wherein saidaverage circuit judges said state according to said state signal so asto calculate the average value of said reproduction signal in saidstate.
 10. The data reproducing device as claimed in claim 7, whereinsaid follower determines at least one expected value according to saidaverage value, the expected value being used in said Viterbi decodingalgorithm, so as to supply said expected value to a Viterbi detector.11. The data reproducing device as claimed in claim 7, wherein saidfollower adjusts the fluctuation amount of the direct current componentaccording to said average value.
 12. The data reproducing device asclaimed in claim 7, wherein said state is one of a peak portion, acenter portion and a bottom portion of said reproduction signal.
 13. Amagneto-optical disk device for reproducing data according to astate-transition pass selected as being most likely according to aViterbi decoding algorithm from a reproduction signal supplied from arecording medium having data recorded according to a partial-responsewaveform, the device comprising: a condition detector detecting at leastone state of said reproduction signal according to data used forselecting said state-transition pass, the data being supplied from aViterbi detector; an average circuit calculating an average value ofsaid reproduction signal in said state detected by said conditiondetector; and a follower following a fluctuation amount of a directcurrent component of said reproduction signal according to said averagevalue.